Measuring based on a vibrating sensor of angular velocity has proved to be a reliable method with a simple principle of operation for the measuring of angular velocity. In a vibrating sensor of angular velocity, a certain known primary motion is induced and maintained in the sensor. The desired movement to be measured by means of the sensor is then detected as a deviation of the primary motion.
An external angular velocity affecting the sensor in a direction perpendicular to the resonators' direction of motion will cause a Coriolis force in the seismic mass, in a direction perpendicular to its direction of motion. The Coriolis force, which is proportional to the angular velocity, is detected capacitively, for example, from the vibration of the mass.
Particularly in the consumer electronics market there is great demand for extremely low priced and small sensors of angular velocity. In such applications, the performance of the sensor, such as the zero point stability or the vibration sensitivity, is of marginal importance.
Present silicon micromechanical sensors of angular velocity on the market are much too bulky, complicated and expensive for such applications. Only small and cheap sensors of angular velocity of ceramics or quartz intended for optical picture stabilization in cameras come even close to the size objectives or the cost level needed in these applications.
However, using the technologies mentioned above, it is extremely difficult to achieve sufficient impact resistance to allow dropping the component on a hard surface without the component braking.
Below, prior art is described with exemplifying reference to the appended drawings, of which:
FIG. 1 shows a diagram of the functional structure of a vibrating micromechanical sensor of angular velocity according to prior art, and
FIG. 2 shows a block diagram of the analog system electronics of a typical sensor of angular velocity according to prior art.
FIG. 1 shows a diagram of the functional structure of a vibrating micromechanical sensor of angular velocity according to prior art. The depicted vibrating micromechanical sensor of angular velocity according to prior art comprises a mass 1, supported at an activation frame 2 in the direction of the X-axis by means of springs 4, 5. Said activation frame 2 is further supported at a support structure 3 in the direction of the Y-axis by means of springs 6, 7.
In the illustrated vibrating micromechanical sensor of angular velocity according to prior art, the mass 1 in the middle, and the activation frame 2 surrounding it, are activated into a primary motion in the direction of the Y-axis, enabled by the springs 6, 7 supported at the body 3. The detection axis formed in the direction of the X-axis by means of the spring suspension 4, 5 of the mass 1 to the activation frame 2, is perpendicular to the primary motion.
When the structure vibrating in the primary motion is turned in relation to the Z-axis perpendicular to the surface xy-plane, the mass 1 in primary motion experiences a Coriolis force in the direction of the X-axis perpendicular to its direction of motion. Thus the detection springs 4, 5, in addition to defining the damping, further define the amplitude and phase of the vibration of the induced detection motion.
The measuring electronics of a modern sensor of angular velocity are rather complicated. In a typical implementation of the analog electronics, more than ten different blocks are needed even in the simplest case.
FIG. 2 shows a block diagram of the system electronics of a typical sensor of angular velocity according to prior art.
In present sensors of angular velocity, the detection of the Coriolis signal is implemented as a phase-sensitive amplitude detection by demodulating the signal of the detection resonator in phase with the Coriolis signal.
One sensor of angular velocity according to prior art is described in the patent publication U.S. Pat. No. 6,946,695. In said patent publication, the mass of the described sensor of angular velocity is spring suspended symmetrically to the substrate by means of a thin film. In the film serving as a spring, piezoelectric elements are formed out of piezoelectric thin film, by means of which the mass can be activated into a linear primary motion and by means of which this primary motion also can be detected. Additionally, at the film, by proper positioning, third piezoelectric elements are formed, the signal phase of which will change as a function of the angular velocity, which, due to the Coriolis force, displaces the primary motion in a direction perpendicular to the direction of the primary motion and to the direction of the external angular velocity.
The prior art patent publication clearly describes the principle, using phase shift, of measuring angular velocity by means of piezoelectric sensors. The described structure and method are based on the positioning of the piezoelectric elements such, that the third elements, which detect the angular velocity, detect the sum of both the primary motion and the secondary motion caused by the angular velocity, the phase of which is proportional to the angular velocity to be measured.
The structures according to prior art described above are not, however, suitable for use in sensors of angular velocity requiring good resistance to vibrations and impact.
Thus, the object of the invention is to provide a structure for a vibrating sensor of angular velocity, in which a large part of the measuring electronics of the vibrating sensor of angular velocity is implemented in a simpler manner compared to solutions according to prior art.